1. Field of the Invention
The present invention relates to a device for detecting the knocking of an internal combustion engine based on an ionic current that flows through a spark plug during the combustion in the internal combustion engine. More specifically, the invention relates to a device for detecting the knocking of an internal combustion engine by preventing erroneous detection of noise or erroneous detection of knocking in a state in which the engine is being shifted toward producing an increased number of the signals of the knocking level or a decreased number of the signals of the knocking level.
2. Prior Art
In a device for controlling an internal combustion engine, so far, it is accepted practice to judge the occurrence of knocking during the operation and, when the occurrence of knocking is detected, the control quantity for the internal combustion engine is corrected toward the side of suppressing the knocking (e.g., toward the side of delaying the ignition timing) depending upon the amount of knocking in order to prevent damage to the internal combustion engine.
In order to detect the knocking of the internal combustion engine, therefore, there has been proposed a device that utilizes a change in the amount of ions produced during the combustion of the internal combustion engine.
The device for detecting the knocking of the internal combustion engine based on the ionic current is capable of detecting the intensity of knocking in each of the cylinders without using knock sensor, and is effective in decreasing the cost.
In the device of this type, a background level is set for an ionic current detection signal in order to prevent erroneous detection of the knocking caused by noise superposed on the ionic current.
In a device disclosed in, for example, Japanese Patent Laid-Open No. 10-9108, a background level (reference for judging the noise level) operated from the sum of an average value of the detection signal intensities and an insensitive region (offset value) based on the operation condition, has been set for a signal that is obtained by shaping the waveform of a knock current detection signal.
FIG. 6 is a block diagram schematically illustrating a conventional device for detecting the knocking of an internal combustion engine. FIG. 7 is a timing chart illustrating the operation waveforms of signals in FIG. 6 and shows a case where a knock signal Ki is superposed on a waveform-shaped signal Fi of an ionic current detection signal Ei.
In FIG. 6, the ignition device 1 of the internal combustion engine includes an ignition coil having a primary winding and a secondary winding, and a power transistor (both of which are not shown) for interrupting the flow of the primary current i1 (see FIG. 7) into the ignition coil.
The power transistor in the ignition device 1 turns on and off (flows and interrupts) the primary current il to the ignition coil in response to an ignition signal P from an ECU 5, and the ignition coil generates a high ignition voltage V2 (see FIG. 7) through the secondary winding in response to the turn on and off of the power transistor.
Being impressed with a high spark voltage V2 from the ignition device 1, the spark plug 2 generates a spark to ignite the mixture at a predetermined timing in each of the cylinders of the engine.
In order to detect the ionic current that flows across a gap of the spark plug 2 at the time of combustion, the ionic current detecting circuit 3 includes a bias means (capacitor) for applying a bias voltage to the spark plug 2 through the ignition coil in the ignition device 1, and a resistor (both of which are not shown) for producing an ionic current detection signal Ei.
Various sensors 4 include a known throttle opening sensor, a crank angle sensor, a temperature sensor and the like sensors, and produce various sensor signals that represent the operation conditions of the internal combustion engine. For example, the crank angle sensor which is one of the various sensors 4 produces a crank angle signal SGT (see FIG. 7) depending on the rotational speed of the engine.
Various sensor signals inclusive of the ionic current detection signal Ei and the crank angle signal SGT, are input to the ECU 5 that comprises a microcomputer.
The crank angle signal SGT has a pulse edge representing a reference crank angular position in each cylinder, and is used by the ECU 5 for executing various control operations.
The ECU 5 includes a knock detecting means 6 for detecting the knocking based on the ionic current detection signal Ei, and an ignition control means 7 that delays the spark signal P based on the result of detecting the knocking by the knock detecting means 6.
The knock detecting means 6 in the ECU 5 includes a filter means 11 comprising a band-pass filter, a counter means 12, an averaging means 13, an offset means 14, and a comparator means 15.
The filter means 11 includes a waveform-shaping means, and picks up a knock signal Ki in a predetermined frequency band from the waveform-shaped signal Fi (see FIG. 7) of the ionic current detection signal Ei.
The counter means 12 includes a waveform-processing means, and counts the number N of the pulses of the knock signals Ki after their shapes have been processed.
The counter means 12 constitutes a knocking level operation means, and operates the number N of the pulses (signals of the knocking level) corresponding to the knocking state of the engine.
The number N of the pulses (signals of the knocking level) represents the amount of knocking occurring.
The averaging means 13 averages the number N of the pulses to operate an average knocking level AVE.
The offset means 14 offsets the average knocking level AVE and forms a background level BGL (reference for judging the noise level).
The offset means 14 includes an offset operation means for operating an offset value OFS for the average knocking level AVE depending on the operation conditions of the engine, and a background level operation means for operating the background level BGL by adding up the average knocking level AVE and the offset value OFS together.
The comparator means 15 constitutes a knock-judging means, and compares the number N of the pulses (signals of the knocking level) with the background level BGL to judge the knocking state of the engine. When the number N of the pulses exceeds the background level BGL, the comparator means 15 produces the result of comparison representing the occurrence of knocking.
Next, described below with reference to FIGS. 6 and 7 as well as a flow chart of FIG. 8 is the operation of the conventional device for detecting the knocking of the internal combustion engine.
First, the ECU 5 receives a crank angle signal SGT and the like signals from various sensors 4, executes various operations depending upon the operation conditions, and produces drive signals to various actuators such as the ignition device 1 and the like.
For example, the ECU 5 turns the power transistor in the ignition device 1 on and off in response to the ignition signal P to flow and interrupt the primary current i1.
In this case, the bias power source (capacitor) in the ionic current detecting circuit 3 is electrically charged with the primary voltage V1 that generates in the ignition coil when the primary current i1 flows therein.
Further, the primary voltage V1 rises when the primary current i1 is interrupted (corresponds to an ignition timing of the engine), and a further elevated secondary voltage V2 (several tens of kV) is generated from the secondary winding of the ignition coil. The secondary voltage V2 is applied to the spark plug 2 of a cylinder in which the ignition is controlled to burn a mixture in the combustion chamber.
As the mixture burns, ions generate in the combustion chamber of the combustion cylinder, and a bias voltage electrically charged in the capacitor in the ionic current detecting circuit 3 is discharged through the spark plug 2 immediately after the ignition control.
The resistor in the ionic current detecting circuit 3 converts the ionic current into a voltage to produce it as an ionic current detection signal Ei.
Thus, the ionic current that flows through the spark plug 2 after the combustion is input as the ionic current detection signal Ei to the knock detecting means 6 in the ECU 5.
When the engine knocks, the knocking vibration components are superposed on the ionic current, and the waveform-shaped signal Fi of the ionic current detection signal Ei acquires a waveform on which the knocking vibration components are superposed as shown in FIG. 7.
Referring to FIG. 8 illustrating the operation for processing the ionic current detection signal Ei, the filter means 11 of the knock detecting means 6 in the ECU 5 picks up the knock signals Ki only from the waveform-shaped signals Fi of the ionic current detection signals Ei (step S1).
The counter means 12 shapes the waveforms of the knock signals Ki to convert them into a knock pulse train Kp, and counts the number N of the pulses in the knock pulse train Kp (step S2).
The number N of the pulses is strongly related to the intensity of knocking and is used for judging the knocking as will be described later and is, further, used for updating the background level BGL in the next time.
That is, the comparator means 15 in the knock detecting means 6 compares the number N of the pulses with the background level BGL that has been operated in the previous time, and judges whether the number N of the pulses is larger than the background level BGL (step S3).
The number N of the pulses increases with an increase in the intensity of knocking and, hence, the comparator means 15 judges the occurrence of knocking and the intensity of knocking based on the number N of the pulses.
When it is judged at step S3 that N greater than BGL (i.e., YES), the ignition control means 7 operates a delay control quantity for delaying the ignition timing (for suppressing the knocking)(step S4). When it is judged at step S3 that Nxe2x89xa6BGL (i.e., NO), the ignition control means 7 operates an advance control quantity (step S5).
Here, the ignition control means 7, at step S4, makes a reference to the delay correction quantity in the ignition control of the previous time and of this time, and, at step S5, makes a reference to the delay correction quantity in the ignition control of the previous time, thereby to operate the control quantities.
When the state N greater than BGL (knock is occurring) is consecutively judged at step S3, the delay quantities are successively added up, but are no longer added up at a moment when it is judged that no knocking is occurring.
The background level BGL (predetermined number of pulses) that serves as a reference for judging the knocking varies depending on the rotational speed of the engine and the level for shaping the waveforms of the detection signals Ei, but is set to a value of, for example, about 5 to about 20.
When the knocking is detected by the comparator means 15 based on the number N of the pulses, the control quantity is corrected toward the side of suppressing the knocking (i.e., the ignition is optimized for the cylinder in which the knocking is occurring) in order to effectively suppress the knocking.
On the other hand, the averaging means 13 in the knock detecting means 6 averages (filters) the number N of the pulses, and operates an average knocking level AVE by using the following formulas (1) and (2) (step S6).
AVE=AVE(nxe2x88x921)xc3x97KF+NPxc3x97(1xe2x88x92KF)xe2x80x83xe2x80x83(1)
NP=max {Nxe2x88x92BGL(nxe2x88x921), 0}xe2x80x83xe2x80x83(2)
In the formula (1), AVE(nxe2x88x921) is an average knocking level AVE of the previous time, and KF is an averaging coefficient (0 less than KF less than 1) and in the formula (2), BGL(nxe2x88x921) is a background level BGL of the previous time.
The offset means 14 adds an offset value OFS to the average knocking level AVE to operate the background level BGL according to the following formula (3) (step S7),
BGL=AVE+OFSxe2x80x83xe2x80x83(3)
Finally, the ECU 5 stores the background level BGL operated according to the formula (3) in the offset means 14 as a reference for comparison for judging the knocking of when the ignition is controlled in the next time (step S8), and the processing routine of FIG. 8 ends.
Next, described below with reference to FIGS. 9 and 10 is the operation for detecting the knocking of when the average knocking level AVE has shifted (increased or decreased).
In FIGS. 9 and 10, the abscissa represents the time and the ordinate (level in the form of a bar graph) represents the number N of the pulses, and there are shown the number Pn of the pulses corresponding to the noise level and the number Pk of the pulses corresponding to the knocking level.
In these drawings, further, the solid curves represent changes in the average knocking level AVE with the passage of time, dotted curves represent changes in the offset value OFS with the passage of time, and dot-dash chain curves represent changes in the background level BGL (=AVE+OFS) with the passage of time.
Here, the offset value OFS (dotted line) remains constant since there is no change in the operation conditions.
FIG. 9 illustrates changes with the passage of time of when the average knocking level is shifted from a reference region (steady state) into a first predetermined region on the decreasing side and is returned again to the reference state.
FIG. 10 illustrates changes with the passage of time of when the average knocking level is shifted from the reference region into a second predetermined region on the increasing side and is returned again to the reference state.
In FIG. 9, the background level BGL (level for judging the knocking) based on the number N of the pulses (signals of the knock level) in the reference region is changing relatively stably and properly.
When the pulses are detected in a number Pk corresponding to the knocking level, therefore, the knocking is properly judged relying on N greater than BGL. Further, when the pulses are detected in a number Pn corresponding to the noise level, the noise is properly judged relying on Nxe2x89xa6BGL.
When the average knocking level AVE is shifted to the first predetermined region as shown in FIG. 9 due to a change in the ionic current detection system inclusive of the spark plug 2 with the passage of time, however, the steady noise level contained in the knock signals Ki decreases, whereby the average knocking level AVE decreases and the background level BGL decreases, too, following the average knocking level AVE.
In the first predetermined region, therefore, the background level BGL does not properly change, whereby the number Pn of the pulses of the noise level exceeds the background level BGL, and the judgement is incorrectly rendered to be that the knocking is occurring.
In FIG. 10, further, when the average knocking level AVE is shifted from the reference region to the second predetermined region due to a change in the ionic current detection system inclusive of the spark plug 2 with the passage of time, the steady noise level contained in the knock signals Ki increases, whereby the average knocking level AVE increases and the background level BGL increases, too, following the average knocking level AVE.
In the second predetermined region, therefore, the background level BGL does not properly change, whereby the number Pk of the pulses of the knocking level becomes smaller than the background level BGL, and the signals are incorrectly judged to be the noise signals.
According to the conventional device for detecting the knocking of an internal combustion engine as described above, the offset value OFS remains constant so far as there is no change in the operation conditions. Therefore, the background level BGL becomes improper in the first or second predetermined region, making it difficult to correctly judge the knocking.
That is, in the first predetermined region, the number Pn of the pulses of the noise signals of when no knocking is occurring is erroneously judged to be the number Pk of the pulses of when the knocking is occurring and in the second predetermined region, the number Pk of the pulses of when the knocking is frequently occurring is erroneously judged to be the number Pn of the pulses of the noise signals.
The present invention was accomplished in order to solve the above-mentioned problems, and its object is to provide a device for detecting the knocking of an internal combustion engine, which maintains the background level at an optimum value irrespective of a state into which the signals of the knocking level have shifted and, hence, prevents the erroneous detection of noise or the erroneous detection of knocking when the signals of the knocking level have shifted into the increasing side or the decreasing side, enhancing the reliability.
A device for detecting the knocking of an internal combustion engine according to the present invention comprises:
various sensors for detecting the operation conditions of an internal combustion engine;
an ionic current detecting means for detecting the ionic current that flows through a spark plug during the combustion in said internal combustion engine;
a filter means for picking up knock signals from said ionic current;
a knocking level operation means for operating signals of the knocking level corresponding to the knocking state of said internal combustion engine based on said knock signals;
an averaging means for operating an average knocking level by averaging said signals of the knocking level;
an offset operation means for operating an offset value of said average knocking level depending on the operation conditions of said internal combustion engine;
a background level operation means for operating a background level by adding up said average knocking level and said offset value together; and
a knock judging means for judging the knocking state of said internal combustion engine by comparing said signals of the knocking level with said background level;
wherein provision is further made of:
a predetermined region judging means for judging said average knocking level that lies in a predetermined region; and
an offset correction means for correcting said offset value depending on the result of judgement by said predetermined region judging means; wherein
said predetermined region judging means judges said predetermined region when said average knocking level is in an increasing state or in a decreasing state compared to a reference region; and
said offset correction means corrects said offset value toward a direction to cancel the increment or the decrement of said average knocking level depending on the result of judgement by said predetermined region judging means, and corrects said background level to an optimum value.
In the device for detecting the knocking of an internal combustion engine according to the present invention, provision is made of an offset correction inhibition means for inhibiting the processing by said offset correction means when the rotational speed of said internal combustion engine is in a low rotational speed region lower than a predetermined rotational speed.
In the device for detecting the knocking of an internal combustion engine according to the present invention, said offset correction means selectively sets an offset correction coefficient depending upon the result of judgement by said predetermined region judging means, and said offset means corrects said offset value by using said offset correction coefficient.
In the device for detecting the knocking of an internal combustion engine according to the present invention, said offset correction means sets said offset correction coefficient to a value larger than 1 when said average knocking level lies in a first predetermined region which is smaller than a lower-limit value of said reference region, and sets said offset correction coefficient to a value smaller than 1 when said average knocking level is larger than an upper-limit value of said reference region.
In the device for detecting the knocking of an internal combustion engine according to the present invention, said averaging means includes a second averaging means that sets a reflection factor of said signals of the knocking level to a large value on a side where said average knocking level increases, and said predetermined region judging means judges said predetermined region based on a second average knocking level operated by said second averaging means.